For the scene where Dorothy sits on Ruby's back while the latter runs in werewolf form, Teri Reeves rode a mechanical apparatus, which was CGIed into a wolf in post-production.
The scene in "Our Decay" where Zelena masquerades as Mother Superior was filmed with Keegan Connor Tracy and a body double with the same costume and hairstyle.
The original Sorcerer's mansion filming location Cecil Green Park House at the University of British Columbia, was not used for its Underbrooke counterpart. West Point Grey Community Centre in Vancouver was used instead.
"Mother" is the twentieth episode of Season Four of ABC's Once Upon a Time. It was written by Jane Espenson, and directed by Ron Underwood. It is the eighty-sixth episode of the series overall, and premiered on May 3, 2015.
Adam Horowitz is a fan of the singer Bruce Springsteen. "Darkness on the Edge of Town" shares its name with a song from the rock star's 1978 album of the same name.
Vancouver's Stanley Park doubles as the Storybrooke town line for the opening scene by the ice wall and the scene where Robin and his family leave Storybrooke. A blue-screen was used for Elsa's ice wall, which was created in post-production via digital effects.
Goof: As Anita comes out to congratulate Quinn for bringing her daughter back, the wide shot films the missing roof of the underground castle, revealing the walls of the sound stage.
This episode "Fruit of the Poisonous Tree" is one of seven episodes of the entire series to not feature a co-starring cast member. The other are "Red-Handed", "The Stable Boy", "Into the Deep", "A Curious Thing", "Poor Unfortunate Soul" and "Her Handsome Hero".
While shooting one of the hospital scenes where David and Mary Margaret is in his room, Josh Dallas kept falling asleep. Ginnifer Goodwin and the crew attempted to prank him by sneaking out and sending someone in to say it was 6am the next day, but he woke up as they were tip toeing away.